212 NEAR AND DISTANT SIGHT. 
as, for example, volatile alkali and acid having formed sal-am- 
moniac, becomes a distinct spherical element in his figure, and 
affords a new compound with copper. 
I would not venture to depart from the wise reserve of the 
learned author of this memoir, by speculating upon the crys- 
talline forms capable of being produced in combinations of 
elements subordinate to each other in simplicity, according to 
Dr. Fordyce’s notion, which appears to agree wdth the pro- 
cesses of nature ; nor by considering the variations which 
might be assumed, or perhaps deduced from the relative mag- 
nitudes, densities, definite proportions in mass and electric pola- 
rities (if such can be supposed in simple particles of bodies.) 
I would^ only hint, that, though an attempt to establish these 
doctrines w'ould undoubtedly be premature, it may, neverthe- 
less, be expected, that considerable advantages would be de- 
rived from their organization and arrangement. 
vir. 
Olscrvalions relative to the near and dUtant Sight of different 
Persons. By James Wake, Esq. F. R. S. From the Philo- 
sophical Transactions for\^V6. 
Commcnce- 
rif-nt of near- 
siijlit is early ; 
of distant 
sight late. 
V 11 '(HE fact that near-sightedness most commonly commences 
-i- at an early period of life, and dislanr-sightcdness gene- 
rally at an advanced age, is universally admitted. Exceptions, 
however, to these rules, so frequently occur, that I flatter my- 
self a brief statement of some of the coincident circumstances 
attendant on these diflerent imperfections in vision, ipay not be 
found w'holly undeserving the attenrion of the Royal Society. 
Near-sightedness usually comes on between the ages of ten 
and eighteen. The discovery of it most commonly ni-i.-cs from 
^accident; and, at first, the inconvenience it occasions is so 
little, that it is not improbable the imperfection would remain 
9 ltogelher unnoticed, if a comparison were not instituted with 
tha 
